Variable capacitance d.c.-a.c. converter



May 23, 196.7 l .VZVENMVON ABE lv51-AL. 3,321,696

VARIABLE CAPAClTANCE D C -A C CONVERTER Filed nec. 24, 196:5

f FIG. 2

FIG.- looooI (1C /7 AMPLIFIER INTERMITTENT HEATING APPARATUS FILTER V3 FILTER l TEMPERATURE m INVENTORS 'ZQNMQM Abr. KILSLUMI TqlCMi Kwant@ HAMMAM. VMM@ Fna-*IWI* MMM g www VUnited States Patent() 3,321,696 VARIABLE CAPACITANCE D.C.A.C.

CONVERTER Zenmon Abe and Katsumi Takami, Kitatarna-gun, Tokyoto, Kiyokata Matsuura, Chiiiusa-ku, Nagoya-shi, and Yoshiol Furuhata, Hachioji-shi, Japan, assignors to Kabushiki Kaisha Hitachi Scisakusho, Tokyo-to, Japan, a joint-stock company of Japan Filed Dec. 24, 1963, Ser. No. 333,006 Claims priority, appli7catign Japan, Dec. 28, 1962,

,180 4 Claims. (Cl. 321-43) This invention relates to conversion of a direct current to an alternating current, and more particularly it relates to new D.C.-A.C. converter, the principle of which differs from those of D.C.A.C. converters of known type among which are mechanical choppers, transistor choppers, -photoconductive choppers, Hall-element type converters, magnetic modulators.

More specifically, the present invention concerns D.C.- A.C. converter wherein the substantial variation -of the dielectric constant of a ferroelectric material due to temperature variation in the vicinity of the Curie point (T6) is utilized as a variation Iof electrostatic capacity.

It is a general object of thepresent invention to provide D.C.-A.C. converter having highly desirable features as will become apparent hereinafter.

The nature, principles, and details of the invention will be best understood by reference to the following description taken in conjunction with the accompanying drawings in which like parts are designated by like reference numerals, and in which:

FIG. 1 is a graphical representation indicating the temperature-dependence of dielectric constant of a triglycine sulfate single crystal whic-h is one example of the converter element according to the invention;

FIG. 2 is a block diagram indicating the composition and arrangement according to the principle of the converter according to the invention;

FIGS. 3 and 4 are diagrammatic elevational views indicating a preferred embodiment of the invention;

In general, a ferroelectric material or antiferroelectric material consisting of a substance such as barium titanate, triglycine sulfate, and lead zirconate or a solid soluti-on of such a substance and another Icompound has a dielectric constant which varies greatly with temperature. This variation is particularly abrupt as is indicated in FIG. 1 (wherein triglycine sulfate is taken as an example). It is apparent from this curve that, in the case of a triglycine sulfate single crystal, when the temperature is decreased approximately 10 deg. C. from the Curie point (approximately 47 deg. C.), the dielectric constant drops to a value which is approximately /oo of that at the Curie point.

Accordingly, if such a ferroelectric material or antiferroelectrics is maintained at Ia temperature in the vicinity o'f the Curie point and then cooled with a certain constant period, or is maintained at a certain temperature below the Curie point and then heated with a constant period to the vicinity of the Curie point, its dielectric constant will vary substantially, `for exam-ple, by approximately decades, in response to the temperature variation.

Therefore, lby constructing a capacitor of a `ferroelectric material single crystal, applying a direct-current input between the electrodes of the capacitor, and, .at the same time, causing the temperature to vary with a certain constant period in the vicinity of the Curie point, the capacitance of the capacitor will vary widely in accordance with the variation of the dielectric constant, and the input direct current will be converted into an alternating current of the said period.

vThe converter element need not be limited to merely a single crystal of a 4ferroelectric material or antiferroelectric material, a ceramic capacitor consisting of a solid solution of various ferroelectric materials or antiferror electric material also being usable. In the case of such a solid solution, the Curie point can be present at a desired temperature by suitably blending the composition of the solid solution. Therefore, a solid solution of the optimum Curie -point in accordance with the performance of the heating and cooling device 1for the converter element is selected. In some cases, when the temperature of a ferroelectric material is caused to vary in `a range between a temperature below the Curie point and the Curie point, the input signal remains in the capacitor as a residual voltage. In such a case, this adverse eiiect can lbe almost entirely removed by causing the temperature variation to take place in a range between a temperature above the Curie point and Curie point.

In order to indicate still more fully the principle and details of the present invention, the Vfollowing description of the principles and of a preferred embodiment thereof lis presented.

One example -according to the invention of an apparatus, as shown in FIG. 2, which accomplishes temperature variati-on of a converter element 3 consisting of a ferroelectric material comprises, essentially, a high-frequency intermittent heating apparatus 4 for heating the element 3, an A.C. amplier 7, and filters 5 and 6 respectively for suppressing transfer of high-frequency energy to the input side and to the amplifier of the succeeding stage. Direct-current input terminals 1 and 2 are connected to the iilter 5, and alternating-current output terminals 8 and 9 are provided on the output side of the A.C. amplier 7. Furthermore, the filter 5 functions additionally also as a lter Ifor the mixed noise within the signal.

When, in the apparatus as described above, the con.- verter element .is subjected to high-frequency heating (dielectric heating) in an intermittent manner with a period in accordance with the thermal time constant thereof at a temperature in the vicinity of its Curie point, the capacitance of the element varies widely, and the input direct current is converted into alternating current,whereby the desired operation is obtained.

FIG. 3 shows a part of the device wherein, in order to cause the heat response of the' converter element 3 to be rapid, the element is mounted on a Peltier element, which yis composed of diiferent metals P and N and, as is well known, and effects heat absorption and heat generation in accordance with the direction in which a direct current iiows therethrough. The converter element 3 is provided with electrode terminals 10 and 11 and is disposed on and in close contact with the junction of the metals P and N. By this construction, when an alternating current corresponding to the thermal time constant of the Peltier element is caused to flow therethrough, heat absorption and heat generation takes place at its junction between the metals, and the capacitance of the converter element 3 in close contact with these metals varies widely. Accordingly, the D.C. input current applied to the terminals 10 and 11 is converted into an A C. current of a period equal to that of the A C. current flowing through the Peltier element.

When it is necessary to maintain the converter element at a constant temperature and to impart a temperature variation with this temperature as a standard reference, a constant direct current may be caused to liow through the Peltier element, and an alternating current for the purpose of imparting temperature variation may be applied in a superimposed manner on the direct current.

The thermal response of the converter element 3 can be further increased by projecting an infrared spot intermittently on the converter element' 3 during its cooling. In one arrangement for this purpose as shown in FIG. 4, infrared rays from an infrared lamp 12 are focused by a lens 13 to form an infrared spot on the converter elementV 3 in -accordance with intermittent control by a shutter device 14.

In the apparatus of the above-described arrangement, the converter element 3 is cooled by the Peltier element P, N or is air cooled, and the shutter 14 is intermittently opened and closed to project a heat-ray (infrared-ray) spot onto the converter element 3, whereupon the element 3 is subjected t-o extremely rapid heating, and the period of D.C.A.C. conversion becomes very short.

As an alternative means for heating, an apparatus wherein ultrasonic heating is utilized can also .be used.

In a D.C.-A.C. converter as described above -in which a ferroelectric material is utilized, since the capacitance of the converter element is widely varied, the D.C.4A.C. conversion efficiency is extremely high, it being theoretically possible to cause this efciency to be of the order of 90 percent. The numerical value of this eiciency may be indicated by the following example of actual result. When, in an apparatus as described above, infrared ray was projected intermittently at one-second intervals on a ceramic capacitor (converter element 3) which initially indicated a capacitance :9860 pf. at 18 C., this capacitor was progressively heated, and its capacitance decreased, reaching a substantially steady state after approximately seconds. At this time, the capacitance of the capacitor varied between approximately 7,300 pf. and 5,020 pf., and the quantity of this variation AC was conrmed to be of the order of approximately 2,000 pf. Accordingly, the conversion (eiciency) in the case is calculated as follows:

For comparison, it may be mentioned that the conversion efiiciency of a conventional converter of variable capacitance type (vibrating reed) is of the order of several percent. Furthermore, since the output impedance with respect to alternating -current of such a conventional variable capacitance type converter is between several tens to several hundreds of megohms, it has heretofore been always necessary to use vacuum tubes in the preamplifier. In the case of a ferroelectric material capacitor, however, since e is as high as several thousands to tens of thousands, the capacitance is high, and it is possible to select the A C. output impedance t-o be of the order of several kilo-ohms. Therefore, this type of capacitor is advantageous in that conversion can be fully accomplished even when the preamplifier is a transistor A.C. amplifier.

As described above, in the converter according to the invention, the source of exciting energy for the converter element is temperature, which is of a nature completely diiferent from that of electricity and magnetism. Accordingly, since adverse electrical noise from electric lsource of a converter are extremely small, an ideal converter can be obtained.

It should be understood, of course, that the foregoing disclosure relates to preferred embodiments of the invention and that it 4is intended to cover all changes and modifications of the examples of the invention herein chosen for the purposes of the disclosure, which do not constitute departures from the spirit and scope of the invention as set forth in the appended claims.

What is claimed is:

1. A variable capacitance type D.C.-A.C. converter comprising a converting capacitor made of ferroelectric material; means to apply an input direct current to said capacitor; means to cause the temperature of said ferroelectric material to vary periodically in the vicinity of the temperature at which the dielectric constant of said material varies greatly with temperature; means to take out from said capacitor an alternating current having a period corresponding to the period of said temperature variation.

2. The variable capacitance type D.C.A.C. converter according to claim 1, wherein a therrnoelectric device having a Peltier element with an intermetallic junction is provided to which said converting capacitor is secured, and means to cause the current in said thermcelectric device t-o vary.

3. The variable capacitance type D.C.A.C. converter according to claim 1, wherein a thermoelectric device having -a Peltier element with a heat absorption side is provided to which said converting capacitor is secured, thereby maintaining the mean temperature of said capacitor substantially constant, and means to intermittently project a light .beam onto the capacitor.

4. The variable capacitance type D.C.-A.C. converter according to claim 1, wherein said converting capacitor is made of antiferroelectric material..

References Cited by the Examiner UNITED STATES PATENTS 2,648,823 8/1953 Kock et al 317-247 X 3,054,942 9/1962 Searcy et al. 3-23-93 X 3,062,999 11/'1962 Brown 323-68 X 3,065,402 1v1/1962 ILandauer 323--69 3,149,298 9/'1964 Handelman 3-38-22 3,252,013 5/1966` Stanton 307-117 X 3,259,763 7/1966 Appleton 307--117 JOHN F. COUCH, Primary Examiner.

W. M. SHOOP, Assistant Examiner. 

1. A VARIABLE CAPACITANCE TYPE D.C.-A.C. CONVERTER COMPRISING A CONVERTING CAPACITOR MADE OF FERROELECTRIC MATERIAL; MEANS TO APPLY AN INPUT DIRECT CURRENT TO SAID CAPACITOR; MEANS TO CAUSE THE TEMPERATURE OF SAID FERROELECTRIC MATERIAL TO VARY PERIODICALLY IN THE VICINITY OF THE TEMPERATURE AT WHICH THE DIELECTRIC CONSTANT OF SAID MATERIAL VARIES GREATLY WITH TEMPERATURE; MEANS TO TAKE OUT FROM SAID CAPACITOR AND ALTERNATING CURRENT HAVING A PERIOD CORRESPONDING TO THE PERIOD OF SAID TEMPERATURE VARIATION. 